Embodiments of the present specification relate to an electric machine, and more particularly to a permanent magnet based electric machine having a rotor and/or stator with enhanced mechanical balance and stress distribution.
As will be appreciated, the term electric machine is generally used to refer to a machine such as a motor or a generator having a rotor and a stator. Non-limiting examples of the electric machines include a radial field electric machine, an axial field electric machine, a transverse field electric machine, and the like. Typically, such electric machines include a stator and a rotor that is movable, for example, rotatable, with respect to the stator. Also, the rotor and/or stator include laminates stacked along an axial direction of the electric machine. Electric machines, such as the radial field electric machines, are currently being used in a variety of applications including, but not limited to, electric pumps such as electric submersible pumps (ESPs). Typically, the electric machine employs permanent magnets in the stator and/or rotor. The ESPs that employ permanent magnet based electric machines (e.g., motor) have been found to be more efficient and powerful in comparison to the ESPs that employ induction motors.
Further, the length of the electric machine in one dimension is often larger than the maximum feasible size of a permanent magnet, more particularly, in case of high aspect ratio ESPs. Moreover, while the diameter of the electric machine for use in such a high aspect ratio ESP is in a range of about 90 mm-250 mm, a length of the electric machine may be in the range of about 3 meters. However, obtaining permanent magnets that match the length of the electric machine is an onerous and expensive task.
Currently, the desired length of the permanent magnet is achieved by stacking a plurality of permanent magnets of smaller lengths. In particular, the permanent magnets are stacked serially, end-to-end along an axis of the electric machine to achieve the desired length of the permanent magnet. Traditionally, adjacently disposed permanent magnets are joined to one another via a butt joint that is perpendicular to an axis of rotation of the rotor. Disadvantageously, such butt joints between the adjacently disposed permanent magnets are not well supported by the laminates of the stator or rotor. The interface between adjacent permanent magnets may fall within a single laminate, which does not provide strong support against lateral movement. Because the permanent magnets arranged in this fashion tend to repel one another and the ends of the permanent magnets deflect laterally in response to the repulsive magnetic effect, the weak support provided to the interface between adjacent magnets may allow the ends of the magnets to damage the laminates and cause mechanical failure of the electric machine. In particular, the repulsion between the adjacent permanent magnets leads to cracks in the laminates of the rotor (or stator) that are disposed in proximity to the butt joint, thereby resulting in reduced lifetime of the electric machine.